: The long term goal of this project is to determine how proprioceptive sensory information at the spinal level is organized and integrated for motor control. The specific aims of this proposal focus on the organization and representation of sensory information in spinal projection pathways to the cerebellum, to areas involved in the control of posture and movement. The dorsal spinocerebellar tract (DSCT) transmits to the cerebellum information derived from sensory receptors in muscle, joints and skin of the hindlimbs. The content of the information transmitted and its utilization by the cerebellum are not known, yet these are central to an understanding of cerebellar function as it relates to spinal motor functions. Current results show that DSCT activity encodes the position and trajectory of the hind foot relative to the hip rather than the individual joint angles. This relationship of DSCT activity to whole-limb geometry appears to depend on a mechanical coupling among joint angles that results from the passive mechanical properties of muscles and ligaments spanning more than a single joint. The coupling results in correlated movements across joints which can change, however, depending on the behavioral state. The question addressed in this proposed research is to determine how the differences in joint angle correlations affect DSCT behavior, and whether the effects are attributable to position and movement alone, or also to forces generated by muscle contractions. That is, does the DSCT monitor parameters related to the mechanical compliance of the limb, or simply to its position and movement? This research is expected to provide new evidence about the role of the nervous system in motor control. Motor control disorders constitute a major health problem with considerable economic consequences. Basic research, such as that proposed here, is needed to understand better the role played by neuronal structures like the spinal cord and cerebellum in the normal control of posture and movement.